By way of background, passenger cars and light trucks generally incorporate a hydraulic brake system including a master hydraulic operating cylinder actuated by the compression of the vehicle brake pedal to supply pressurized hydraulic fluid to a brake assembly at each vehicle wheel. A vast majority of vehicles incorporate a vacuum chamber in combination with the master hydraulic operating cylinder for use as a pressure booster or intensifier. The vacuum generally consists of a tank or housing which interconnects with the vehicle engine to create a vacuum within the tank as is commonly known in automotive power brake systems. When the brake pedal is depressed, the vacuum supplies a pressure amplification to the master operating cylinder to create a sufficient hydraulic brake fluid pressure for vehicle deceleration. However, creation of the vacuum requires that the engine be running. Therefore, with the sudden failure of engine power, the vacuum would fail to provide an increased pressure source from the brake pedal to the master operating cylinder, thus creating difficult if not impossible vehicle braking.
As an alternative, vehicle brake systems may incorporate a standard braking system including a manual hydraulic brake booster or intensifier which relies on the vehicle operator's brake pedal pressure for increasing the brake fluid pressure. Generally the intensifier includes a plurality of actuating piston and cylinder arrangements housed in the master operating cylinder which force the fluid through a pressure boosting chamber.
For example, U.S. Pat. No. 3,393,510 to Kinsey, issued Jul. 23, 1968, discloses a manual hydraulic brake system including a master operating cylinder for pressurizing hydraulic brake fluid and forcing the pressurized fluid through a plurality of fluid lines to a wheel brake assembly. The master cylinder comprises a housing containing a first master piston and cylinder arrangement actuated by brake pedal force. The master cylinder housing further encloses a secondary cylinder in fluid communication with the master cylinder and encompassing a floating secondary piston. A fluid reservoir supplies hydraulic fluid through fluid passageways to each of the cylinders. In operation, the vehicle occupant depresses the brake pedal to actuate the master piston and force the hydraulic brake fluid from the master cylinder to the secondary piston/cylinder arrangement. The secondary piston is subsequently forced into the secondary cylinder and forces the hydraulic fluid through an outlet in the master cylinder housing to a brake fluid line to supply the pressurized fluid to each wheel brake assembly. The secondary piston and cylinder arrangement has a smaller area and fluid volume capacity as compared to the master piston and cylinder arrangement thus providing an increase in fluid pressure as the fluid is acted upon by the series of pistons and forced through the respective cylinders.
Similarly, U.S. Pat. No. 1,897,230 to Bowen, issued Feb. 14, 1933, discloses a manual hydraulic braking system including a master housing encompassing a master piston and cylinder arrangement actuated by depression of a brake pedal. The housing includes a fluid reservoir for supplying fluid to the master cylinder. Upon depression of the brake pedal, the master piston is forced axially along the cylinder to force the hydraulic fluid through an outlet in the master cylinder. The master cylinder outlet is in fluid communication with a fluid channel leading to a secondary piston and cylinder arrangement also enclosed within the master housing. The hydraulic fluid exiting the master cylinder actuates the secondary piston to force the piston axially along the secondary cylinder. The secondary piston and cylinder arrangement has a cylinder area less than the area of the master piston and cylinder arrangement to thereby decrease the volume of fluid flow and thus increase the pressure of the hydraulic fluid as the fluid flows from the master cylinder to the secondary cylinder. The hydraulic fluid is then forced through an outlet in the secondary cylinder and supplied via a brake line to a wheel braking assembly.
As can be appreciated, the addition of a secondary piston and cylinder arrangement within the housing of the master operating cylinder greatly increases the size and fluid volume requirements within the housing to the extent that the master operating cylinder becomes cumbersome and space consuming within the vehicle engine compartment. Furthermore, the master operating cylinder is generally mounted to the firewall within the vehicle engine compartment to provide for direct in-line attachment with the brake pedal linkage. Due to the increased size and weight of the master cylinder, because of the secondary piston and cylinder arrangements, it becomes difficult to assemble and mount the master operating cylinder to the firewall. Furthermore, with the elimination of the power vacuum pump preceding the master operating cylinder, the brake pedal force and travel required upon depression greatly increases to provide sufficient fluid pressure for vehicle braking.